Wire rope - why not aluminum? 1

[neomoses]

I'm in a DFM class at the moment and am actually trying to use all of the 'tools' they have taught us to this point to select a material and process for manufacturing all the parts in our design.

So.... we're stuck at the wire rope (cable). All of the material properties are pointing us in the direction of an aluminum wire rope, but when we look at what's available in production today, I see no off-the-shelf alumiminum wire rope. The only criteria we can find at the moment to discount aluminum would be if we chose to go with infinite life rather than a design life of 10^7 cycles.

Can someone give me some other good reasons why aluminum is not used as a wire rope material today?

Bryan

 

[rorschach]

CoryPad, that violates everything I have ever been taught about Aluminum. I'm not saying you are wrong, just that all of the data I've ever been exposed to tells me that there is no stress level that will not result in fatigue at some point. In this, Aluminum is different from steel as I have always been taught. I really need to take some time and go through your links throroughly.

 

[NickE]

rorschach- from my casual exposure to what CoryPad has said here is my understanding.

Al-alloys do have an endurance limit. The stress levels that are required to provide an infinite life are just very small.

And the endurance limit is not generally seen when testing to 10^6 or 10^7 cycles.

 

[Kwan]

Correct. It's all relative to what you define infinite life as. For example, peanut brittle under cyclic stress probably won't last very long even with very low stress levels. However, if the stress level is keep very very low, then it's possible to show a life of say one month. If it's shelf life is only 2 weeks (ie: you should eat it before the end of the shelf life) then we can say it has an endurance limit because it only has to last two weeks. My disclaimer: don't use peanut brittle to design structure.

 

[Compositepro]

I've been following this thread and would like to add some things. The steel used in wire rope can have a tensile strength of over 350,000 psi because wire making is a perfect process for maximizing the strength of steel. Aluminum has very poor abrasion resistance. It is a very active metal and is only protected by a oxide layer that forms quickly and provides amazing protection if it isn't abraded. A wire rope is not merely a material or a structure. It is a machine in that it has moving parts. When a rope is flexed there is very distinct rubing between moving parts, just like in a gear. The company I work for is developing carbon fiber cables.